Refining apparatus or disk refiners of the above-described type are used, for instance, for highly concentrated refining, CTMP, TMP, fluffing and highly concentrated grinding of sack paper and other fibrous material containing lignocellulose. They usually comprise a rotatable refining disk, mounted on a rotor, and a non-rotatable refining disk, mounted on a stator. Refining disks in this type of refining apparatus are composed of refining segments that form refining surfaces. The refining segments are replaced at regular intervals due to considerable wear. They are either mounted directly on the rotor and stator, respectively, or by means of special segment holders. A refining disk may consist of one or more annular refining segments or of several divided, radial refining segments. Refining segments may be in the form of central segments and peripheral segments, the peripheral segments being located outermost along the periphery, and the central segments being located inside the peripheral segments. Between the refining disk/surfaces on the rotor and stator, respectively, is a space in the form of a refining gap.
A serious problem with this type of refining apparatus, particularly when the apparatus first starts up, is that fiber often builds up to a pulp cake between the rotatable parts and the surrounding refiner housing. This pulp cake sometimes tends to become lodged and completely blocks transport of fibers to the outlet. Besides this obvious drawback, the build-up of pulp in the refiner housing also results in a high degree of friction along the periphery of the rotatable parts, due to the high rate of rotation, and also considerable generation of heat which may cause the fibers to carbonize, becoming so hard that the rotor is turned as by a lathe, and may cause breakdown. Even if these problems do not reach this stage, the build-up of pulp causes continuous wear on the outer part of the rotor and the segment holders of the refining disk when used, so that they may break down in the end. The heat generation may also be so high that the rotor and/or the segment holder may melt. According to conventional technology attempts to eliminate these problems entail providing the rotor itself with wings that protrude into the space between the rotor and the outer wall of the refiner housing to keep it clean. However, these wings often give rise to cavitation damage in the attachment between wing and rotor, which may lead to the wing gradually becoming dislodged, with disastrous consequences. To avoid this, regular maintenance must be undertaken, which is naturally associated with costs.
One object of the present invention is to remedy the problems mentioned above.